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100

SODIUM BICHROMATE

(d)  SULPHURIC ACID.    150 c.c. of the solution (= 3 grams of the salt)
are acidified with hydrochloric acid and precipitated with barium chloride,
the barium sulphate being filtered,  washed, dried and weighed as usual:
(BaS04 X 34-335) ^ 3 = % of S03.

(e)  LIME AND MAGNESIA.    150 c.c. of the solution ( 3 grams of salt)
are treated with ammonia l and ammonium oxalate* the calcium oxalate
being ignited and the lime weighed :   (CaO x 100) -7- 3      % <>f CaO.

The filtrate from this determination is treated with ammonium or sodium
phosphate and the precipitate treated us usual : (MgaP-A X 30-036) -;~ 3 =

%ofMgO.

(/) POTASH. 50 c.c. of the solution (~i gram of salt) are treated as
indicated under " Stassfurt Salts " for the determination of alkalies, the
percentages of Na.a() and Ka() being calculated.

(g) CALCULATION OF THE RKSUI.TS. The sulphuric, a.cid is combined
first with lime, then with magnesia, and lastly, if any remains, with potash
and then soda : any remaining magnesium is united with chlorine and 1 lie
rest of the latter with potash and then with soda..

*
* #

Chemically pure sodium chloride, should not: contain, any of the above impurities.

The pure a,ncl refined stUts may contain respectively o? <)M% and about
99'7% NaCl, and always give the reactions of sulphates and calcium sails ; as
a rule they contain traces only of magnesium salts.

Common 6Vf// (for domestic purposes) varies in composition roughly between
the following limits :

Sodium chloride       .......     87 <)<>,|%

Magnesium chloride .         ......     Traces-i-,|%

Magnesium sulphate.        ......    Traces -1-0%

Calcium sulphate     .......    o-3* -i <>%

Sodium sulphate      .......    o--:iu%

Water     .........    o-v-.io-o%

Impurities (insoluble residue, etc.)     ....    Tract's -o-,:<;%

Incrustations from salt-pans, known as j>ro/o, contains hiss sodium chloride
(77-85%) than ordinary salt and also marked proportions of calcium sulphate
(up to about 8%), sodium sulphate (up to 8-,|%)and magnesium sulphate (.-,%).

Common salt generally contains small quantities of boric, add, this being
particularly the ease with certain sails of Italian origin,

fn salt /or soap~boiliTii>, 1% of insoluble impurities and ,:% of earthy salts
(calcium and magnesium chlorides and sulphates) are allowed by the Union ol;
Italian Soapmakers (TO/IT),

SODIUM   BICHROMATE
Na,,CrA -I- 2lU) - 2<)H3 (298)

The pure, salt, forms hygroscopic, red crystals, which lose their water
of crystallisation at 100. The dehydrated salt, is also sold in large quan-
tities in fused masses or crusts, which are contaminated mainly with sodium
sulphate; and insoluble carbonaceous substances. Its value depends on
its content of chromic anhydride. The following tests are made :

1 If the ammonia produces a precipitate (iron, aluminium), this is filtered off and
washed and the filtrate then treated as described.CHLOKINE.   50 c.c. of this solution (= i gram of salt) are titrated